Corona transfer mechanism

ABSTRACT

An electrostatic reproduction machine has an improved transfer mechanism for effecting transfer of a developed image from a photoconductive surface of the machine to a sheet of paper, the mechanism having a plurality of point discharge needles disposed adjacent the photoconductive surface, and a plurality of rotatably mounted rollers located among the needles and which are in contact with the paper during transfer so as to maintain contact between the latter and photoconductive surface.

[ NOV. 11, 1975 3.743.830 7/1973 Takahashi et 250/325 4/1974 Cade et CORONA TRANSFER MECHANISM [75] Inventor: Richard C. Vock, Ontario, N.Y.

Assignee: Xerox Corporation, Stamford,

Primary E.\'aminerRona1d Feldbaum Attorney, Agent, or FirmJames J. Ralabate; Bernard A. Chiama; Earl T. Reichert Conn.

[22] Filed: Nov. 23, 1973 [57] ABSTRACT An electrostatic reproduction machine has an im- Appl. No.: 418,539

proved transfer mechanism for effecting transfer of a developed image from a photoconductive surface of the machine to a sheet of paper, the mechanism having a plurality of point discharge needles disposed adjacent the photoconductive surface, and a plurality of Mi A 3/1 65 W 1 1 0 7 "6 e ""00 n/ 5 5 is Mr. 3 Ya l hf C d Stud .1 U.mF H N 555 References Cited rotatably mounted rollers located among the needles UNITED STATES PATENT S and which are in contact with the paper during transfer so as to maintain contact between the latter and photoconductive surface.

1 37 5 32 2 Claims, 2 Drawing Figures 1 18/636 881 Walkup et a1. 847 1/1964 Norton................ 796 5/1968 Javorik et a1. 214 1/1973 Kaneko et 122 2/1973 Hudson................

US. Patent Nov.11, 1975 SheetlofZ 3,918,403

US. Patent Nov. 11, 1975 Sheet20f2 3,918,403

CORONA-TRANSFER MECHANISM BACKGROUND OF THE INVENTION veloped electrostatic image from a first surface'to a ity of rollers spaced-among the needles to keep the paper in contact with the photoconductive or other surr face containing. the developed image. The rollers are This invention relates generallyto transferringa desecond surface, .but more particularly :.to .a. transfer mechanism utilizing a plurality of @spaced pointdis- 'tion or step. Such amechanism will be described herein in conjunction with an electrostatic reproduction machine. r

In the process of xerography, for example, as disclosed in Carlson Pat. No. 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electriccharge over its surface and is then exposed to the subject matter to be reproduced,

usually by conventional projection techniques. This exposure discharges the plate area in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material such as an electroscopic powder that is brought into surface contact with'the photoconductive .layer and is held thereon-electrostatically in a pattern corresponding tothe electrostatic latent image. Thereafter, the developed xerographicpowder' image is usu-.

through a cycle of sequential operations including charging exposure, developing andtransfer. 'During the cycle, copy is reproduced on the drum or belt and then '7 transferred to a support surface such as a sheet of paper.

Various means and circuits are typically used for effecting transfer of a developed electrostatic image from the xerographic drum to a sheet of paper. One device commonly used is the conventional corona charging device comprised of a length of wire surrounded by a generally U-shaped shield. With such a device, it is often difficult to' keep the paper in contact with the photoconductive surface during the transfer step. This is because electrostatic tacking force is small, which may be due to either high humidity or heavy paper stock. Also, because 0 nodes which may form on the corona wire, there may be uneven charging of the paper. With some transfer systems there may also be pretransfer sparking.

Thus, what is needed is a transfer mechanism which will generate a unifonn charge while keeping the paper in contact with the photoconductive surface so as to result in a uniform transfer of the developed image.

'or other medium to which a developed electrostatic image is to be transferred. The mechanism has a plural preferably, comprised of metal hubs, the peripheries of which are covered with asuitable rubber which is relatively insensitive to humidity and which has the desired resistivity.

BRIEF DESCRIPTIQN'OF THE DRAWINGS FIG. 1. is a schematic side elevation of an electrostatic printing machine utilizing the-present invention;

FIG.- 2 is a perspective view of a transfer mechanism constructed according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The general apparatus of the instant invention is shown herein embodied in an automatic electrostatic printing machine 10 employing a xerographic plate in the form of a drum 12 comprising a photoconductive layer which is placed upon a conductive backing.

Drum 12 is mounted on shaft 14 joumaled in the machine frame (not shown) and is rotated in the direction indicated by thearrow by means of motor causing the drum surface to sequentially pass through a plurality of xerographic processing stations. The support member (e.g., paper) on which an imageis to be fixed is fed to the drum 12 via paper feeding mechanism.

For purposes of the present invention, the several xerographic processing stations positioned in the path of movement of drum 12 as shown in FIG. 1 may be described functionally as follows:

. a charging station A, at which is positioned a coronagenerating device 16 for placing a uniform positive electrostatic charge on the photoconductive layer of the drum surface as the drum is driven in the direction indicated; i an exposure station B, at which a light or radiation pattern of the original document to be reproduced which is supportedon platen 18, is projected onto the drum surface" thereby dissipating the charge found'thereon in the areas exposed so as to form a latent electrostatic image of the original document; a developing station C having a housing generally designated 20, in which a developed material utilizing, in this case, negatively charged toner particles is delivered to the entrance of the development zone from where it is caused to flow in opposition over an upwardly moving portion of the drum surface by means of bucket conveyors system 22, thus enabling the toner particles to contact and adhere to the electrostatic image on the drum surface to form a developed powder image in image configuration of the original document to be reproduced; a transfer station D, at which the xerographic powder image is electrostatically transferred from the drum surface to a sheet of final support material by means of transfer corona generating device (transfer mechanism) 24 which is constructed according to the subject invention, and

a drum-cleaning and discharge station E, at which the drum surface is exposed to a cleaning corona generating device 26 and then contacted by means of a doctor blade 28 to remove residual toner particles which may remain thereon after the transfer operation and where the drum surface is exposed to the source of illumination 30 to effect substantially complete discharge of any residual electro static charge remaining thereon.

Transfer mechanism 24 located at station D sprays the backside of thefinal support material with positive ions, thus producing a charge of sufficient magnitude on the backof the paper to attract the toner from the drum surface to the final support material. A plurality of arcuate-shaped stripper fingers positioned subsequent to the transfer station are arranged to lift the leading edge of the support material from the drum when necessary anddirect the material upwardly. As the drum continues to drive the support material forward,-the fingers strip the material-from th'e drum and guide it into contact with vacuum transport 30. The support material is then caused to move along the vacuumtransport towards fuser assembly 32.

Under the influence of the rotating drum, thesupport material is moved along the stationary vacuum transport 30 into thenip between the upper fuser roller 34 and the lower fuser roll 36 to fix the image. The coacting fuser rolls are arranged 'to apply a pressure-driving force to the sheet of support material positioned therebetween and to forward the sheet at a synchronous speed with the rotating drum surface.

The copy, With the fixed image thereon, is transported through a circular pathof travel, generally referred to as 38 comprising a series of pinch rolls arranged to eitherdischarge a final support material from the apparatus into catch tray-40 or to feed the support material back into a second feed tray 42. Support material stored in'feed tray42 are once again redirected through the xerographic processing stations to form a second or duplex image on the backside thereof.

Referring to FIG. 2, it can be seen that the transfer mechanism 24 is comprised of a plurality of point dischargeneedles' 44. The needles are spaced so as to uniformly charge the paper 46 passing beneath them,- and as can be seen, are preferably arranged so that the tips of the needles are not located directly over the shaft 48, but are located to one side of the shaft with the tips of the needles being located at about the center of the shaft. To assist in effecting uniform transferthe mecharange of to ID ohm em, but preferably around 10* ohm cm.

It has been found that if the humidity is high enough, there is sufficient lateral migration of the charge on the paper to assure uniform charging across the paper 46;

. in this event, the hubs 52 are preferably grounded. in

the event the humidity is not high enough, uniform charging of the paper can be effected by electrically biasing the hubs 52.

While the invention has been described with reference to the structure disclosed, it is not confined to the details set forth, but is intended to cover such modifica- 'tions or changes as maycome within the scope of the following claims.

What is claimed is: 1. An improved' apparatus for effecting transfer of a developed electrostatic image from a first support member to a second support member, the apparatus" comprising a plurality of spaced pointdischarge needles disposed adjacent to the first support member, and

a plurality of rollers disposed .among the needles, the I rollers being mounted in contact ,thefirst support memberand mounted forrotation around a common axis whereby the rollers keep the first, support member and the second support member in contact with each other during transfer. a

2. An improved apparatus as set forth in claim 1,

wherein each of said rollers comprises a metallic hub and a rubber wheel surrounding said hub. 1 a a: it 

1. An improved apparatus for effecting transfer of a developed electrostatic image from a first support member to a second support member, the apparatus comprising a plurality of spaced point discharge needles disposed adjacent to the first support member, and a plurality of rollers disposed among the needles, the rollers being mounted in contact with the first support member and mounted for rotation around a common axis whereby the rollers keep the first support member and the second support member in contact with each other during transfer.
 2. An improved apparatus as set forth in claim 1, wherein each of said rollers comprises a metallic hub and a rubber wheel surrounding said hub. 